1. Field of the Invention
The present invention generally relates to query processing and, more particularly, to managing execution of queries with respect to different data sources.
2. Description of the Related Art
The creation of increasingly powerful computer systems and a continuously improved information technology (IT) infrastructure contribute to a progressive automation of key tasks and processes in today's businesses. As a result, business processes, such as shipping, procurement and staffing, are transformed so as to be conducted electronically. Such electronically conducted business processes are referred to as electronic business (e-business). A generally accepted widely-used form of e-business is electronic commerce (e-commerce). E-commerce permits transactions for a variety of goods and services to be conducted electronically.
However, while use and development of e-business proliferate, unplanned downtimes of computer systems in companies cause losses of thousands of dollars or more per hour to these companies. Accordingly, prevention of unplanned downtime of computer systems becomes a key challenge in today's business world.
To help alleviate the problem of unplanned downtime, many companies employ strategies termed High Availability (HA). A popular HA strategy is to mirror an original computer system, i.e., to make an exact duplicate of the computer system. Thus, when unplanned downtime of the original computer system occurs, the duplicate or mirror system is able to pick up any tasks that could not be completed by the original computer system before the downtime occurred.
However, mirroring a complete computer system is relatively expensive. More specifically, mirroring an original computer system generally requires another set of appropriate hardware, middleware, and software licenses. Accordingly, the expenses for creating a mirror system for the original computer system could equal the cost of the original computer system. In other words, mirroring the original computer system could easily involve expenses of hundreds of thousands of dollars or more for a given company. Furthermore, if the original computer system includes a database(s) which is frequently updated or otherwise modified, each such change must essentially be replicated in real-time to the mirror system so that the mirror system continuously represents an exact copy of the original computer system. This requires intensive and costly maintenance of the mirror system.
Therefore, there is a need for an efficient technique for providing a high-availability system.